Introduction, spread and persistence of Streptococcus zooepidemicus ST-209 in the Icelandic horse population

Curiously, of the 16 culture positive occasions, 12 of these horses remained seronegative to antigen C. In summary, despite all weanlings being exposed to and/or infected by S. equi in this outbreak, minimal to onlymild disease ensued, possibly related to by their failure of a robust immunologic response to portions of the SeM protein (antigen C). Sequencing studies of the S. equi strains involved are ongoing to determine whether genetic deletion events (3) could help explain the reduced clinical severity.